For car P,
v2=u2+2as
484=u2+2as (1)
For car Q,
961=u24+4as
3844=u2+16as (2)
From (1) and (2),
14 as = 3360 ⇒ as = 240 (3)
Multiplying equ (1) by, 8 we get
3872=8u2+16as (4)
On comparing (2) and (4), we get
28=7u2 ⇒ u2=4
∴ u=±2
For car P,
v = u + at (By first equation of motion)
⇒ 22 = 2 + at
⇒ at = 20
For car Q,
v = u + at
31 = 1 + 2a(t – 1)
⇒ 31 = 1 + 2at – 2a
⇒ 2a = 10
∴ a=5 ms2
Put a = 5 ms2 in (3), we get
s=2405=48 m